BACKGROUND: Mothers are a population that engages in low levels of physical activity due to unique barriers to physical activity. As such, there is a need to develop and implement physical activity interventions for mothers that can be delivered in community settings. The objective of this article is to describe the Moms UNITE (Using Networks to Increase Togetherness and Efficacy) for Health walking intervention. This intervention, based on social cognitive theory, is designed to compare a collective efficacy enhanced intervention to a standard intervention for increasing physical activity and secondary outcomes. METHODS: In this 6-week, randomized controlled trial, mothers will be assigned to either the standard or intervention (collective efficacy) group. Both groups will receive the same walking intervention and an evidence-based health education program. Strategies and messages focusing on building collective efficacy will be used in the intervention group. Data will be collected at baseline, post-intervention, and follow-up (after a 3 month no-intervention period) using a mixed methods approach. RESULTS: Quantitative data will include anthropometric measurements, objective physical activity, and questionnaires assessing self- and collective-efficacy. Post-intervention focus groups and weekly process evaluation surveys will describe participants' experiences within the program. CONCLUSIONS: This paper will serve as a theoretical framework for researchers and public health practitioners to develop and implement community-based walking programs for mothers.